To ensure proper function and operation of a firearm, it is desirable and necessary to ensure feeding of cartridges from a magazine into the firearm chamber as smoothly and as quickly as possible as the cartridges are advanced along the magazine. Some common 5.56 mm M4/AR-platform magazines have a rib designed to rest on the case neck of standard 223 and 5.56 mm ammunition. However, when larger caliber ammunition, such as 300 AAC Blackout and 300 Whisper® cartridges are fed from such magazines, the magazine rib frequently rests on a part of the bullet which is 0.308 diameter, rather than the 5.56 mm case neck, which is 0.253 diameter. This forces the cartridges to tilt inward, often causing binding of the rounds if the magazine is loaded past approximately 10 rounds. This binding can cause problems with consistent and arcuate feeding of the rounds from the magazine as the spring within the magazine quickly pushes or urges the next cartridge to the top of the stack. As a result, the rounds can become jammed in the magazine and/or otherwise may not feed properly therefrom. The prior-art solution generally has been to load the cartridges to a shorter-than-optimal overall length or limit use to pointed projectiles with a large radius ogive, often precluding the use of projectiles with a large meplat (flat front).